Electrode for generation of hydrogen

ABSTRACT

An electrode for use in hydrogen generation comprising a conductive base and a coating layer formed thereon of a composition obtainable by thermally decomposing, in the presence of an organic acid, a mixture comprising at least one type of platinum compound.

TECHNICAL FIELD

[0001] The present invention relates to an electrode for use inelectrolysis, in particular, an electrode for use in hydrogen generationwhich is suitably used in the electrolysis of sodium chloride based onan ion exchange membrane method and which exhibits a low overvoltageover a long period of time.

BACKGROUND ART

[0002] In the process of the electrolysis of sodium chloride based on anion exchange membrane method, the reduction of energy consumption is oneof the most important issues. A detailed analysis of the voltageinvolved in the electrolysis of sodium chloride based on an ion exchangemembrane method shows that the voltage includes, in addition to thetheoretically required voltage, the voltage due to the ion exchangemembrane, the overvoltages of the anode and cathode, and the voltagedependent on the distance between the anode and cathode in theelectrolysis vessel.

[0003] As for the overvoltages of the electrodes among these variousvoltages, as far as the overvoltage of the anode is concerned, theso-called insoluble electrode referred to as the DSA (Dimension StableAnode), provided with a coating layer of a platinum group oxide, reducesthe overvoltage to a level lower than 50 mV or less such that no furtherimprovement can be expected.

[0004] On the other hand, as far as the cathode is concerned, suchconventionally used materials as mild steel, stainless steel and nickelexhibit overvoltages ranging from 300 to 400 mV. Accordingly, theactivation of the surfaces of these materials has been studied for thepurpose of reducing the overvoltages.

[0005] Examples include a highly active cathode produced from an oxideby thermal spraying of nickel oxide, cathodes utilizing Raney nickelbased metals, cathodes taking advantage of composite plating with nickeland tin, and cathodes based on composite plating of active charcoal andoxides; all of these cathodes have been attempted to be applied to thecathode for use in hydrogen generation in caustic soda.

[0006] However, for the purpose of reducing the electrolysis voltage, itis necessary to further reduce the overvoltage, and accordinglyelectrodes based on various concepts have been proposed.

[0007] In JP-B-3-75635 (EP129734B), a layer of a heterogeneous mixturecomposed of a platinum group oxide and nickel oxide has been formed as acoating layer on a conductive metal base and thus a cathode having a lowovervolatage has been made.

[0008] In U.S. Pat. No. 4,668,370, composite plating with a noble metaloxide and metallic nickel actualizes a low overvoltage and enhances thedurability of the coating layer. In JP-B-6-33481 and JP-B-6-33492 (U.S.Pat. No. 4,900,419 or EP 298,055B), a composite substance composed ofplatinum and cerium is adopted as an electrode coating material,permitting enhancement of the poisoning resistance against iron.

[0009] In U.S. Pat. No. 5,645,930 and U.S. Pat. No. 5,882,723, rutheniumchloride, palladium chloride and ruthenium oxide are applied onto aconductive base, the base thus processed is calcined in the air, andthereafter subjected to electroless plating with nickel, thus improvingthe coating strength.

[0010] In JP-A-11-140680, an electrode coating layer mainly composed ofruthenium oxide is formed on a metal base, and further a porous andlow-active protective layer is formed on the surface thereof, thusimproving the electrode durability.

[0011] In JP-A-11-158678, an electrode coating layer is formed which isprovided with a coating layer of ruthenium oxide, nickel and a rareearth metal capable of absorbing hydrogen formed on a metal base bypyrolysis, and thus electrolytic oxidation is prevented by maintainingthe cathode at the hydrogen absorbing potential against the reversecurrent caused by the termination of the electrolysis.

[0012] In JP-A-11-229170, an electrodeposited nickel layer is providedin which ruthenium oxide is dispersed, the surface of the layer iscoated with a conductive oxide composed of titanium oxide, and thus theresistance to mercury poisoning is improved.

[0013] However, even in the above described examples, the electrodeoperating life is short so that as matters stand, indeed, furtherelongation of the electrode operating life is an objective.

[0014] In WO01/28714, the interior of the coating layer is made porousand hence the surface area is made larger so that the resistance to theimpurities found in alkali is improved, and a cathode having a lowovervoltage is formed.

DISCLOSURE OF THE INVENTION

[0015] The present invention was achieved for the purpose of overcomingthe above described problems and takes as its object the provision of acathode which is stable in quality, low in overvoltage and excellent indurability by applying a pyrolysis method suitable for mass production.

[0016] As a result of an investigation intended to obtain a cathode inline with the above described object for the purpose of overcoming theabove described problems, the present inventors came to find theexperimental results described below in the course of the investigation.

[0017] (a) Ruthenium oxide and the hydrate thereof are effective as theelectrode active material for an active cathode.

[0018] (b) However, ruthenium oxide is slowly reduced to rutheniumhydrate at the hydrogen generation potential so that a structural changeis caused.

[0019] (c) When ruthenium chloride is thermally decomposed in areductive atmosphere of hydrogen or an inert gas, it is reduced intometallic ruthenium; metallic ruthenium is high in overvoltage, and iseasily exfoliated from the base, thereby resulting in poor durability.

[0020] (d) When the temperature is raised in the pyrolysis, the carbonatoms in oxalic acid exhibit an oxidation effect so that the generationof ruthenium oxide is scarce even for the case where calcination isconducted in an oxidative atmosphere. Additionally, a substance calcinedin the presence of oxalic acid is low in overvoltage and tends tomaintain a stable structure even at the hydrogen generation potential incontrast to the metallic ruthenium generated by calcination in areductive atmosphere, and accordingly can maintain a low overvoltageover a long period of time.

[0021] (e) Compounds of lanthanum, cerium and yttrium themselves arepoor in hydrogen generation activity, but the oxides thereof areconverted from particle shapes into needle shapes during electrolysis,and the needle-shape forms play the role of holding the coating layercomposed of either ruthenium oxide or ruthenium hydrate, thus beingeffective in preventing the physical exfoliation of the coating layer.

[0022] The present inventors perfected the present invention bydiscovering a technique which permits the production of a crystalstructure stable as a coating layer even by pyrolysis in an oxidativeatmosphere with generation of reductive hydrogen, as a result of theinvestigation described above. Herewith, it has become possible toprovide a cathode that is small in the number of constraints forproduction, low in production cost and can maintain a low overvoltageover a long period of time.

[0023] In other words, the present invention is described as follows.

[0024] (1) An electrode for use in hydrogen generation comprising aconductive base and a coating layer formed thereon of a compositionwhich is obtainable by pyrolysis, in the presence of an organic acid, ofa mixture comprising at least one type of platinum group compound.

[0025] (2) An electrode for use in hydrogen generation comprising aconductive base and a coating layer formed thereon of a compositionwhich is obtained by thermally decomposing, in the presence of anorganic acid, a mixture comprising at least one type of platinum groupcompound and at least one type of compound selected from the groupconsisting of a lanthanum compound, a cerium compound and a yttriumcompound.

[0026] (3) The electrode for use in hydrogen generation described abovein (2), wherein the amount of at least one type of compound selectedfrom the group consisting of a lanthanum compound, a cerium compound anda yttrium compound falls within a range from 1/20 to 1/2 mol in relationto one mol of metal component in the above described platinum groupcompound, and the amount of the above described organic acid fallswithin a range from 1/20 to 2 mols in relation to one mol of the metalcomponent in the platinum group compound.

[0027] (4) The electrode for use in hydrogen generation described abovein any of (1) to (3), wherein the above described platinum groupcompound is a ruthenium compound and the above described organic acid isoxalic acid.

[0028] (5) An electrode for use in hydrogen generation comprising aconductive base and a coating layer formed thereon, wherein the coatinglayer is a composition obtainable by thermally decomposing, in an oxygenatmosphere, a mixture comprising a ruthenium compound, oxalic acid in arange from 1/20 to 2 mol and at least one type of compound selected fromthe group consisting of a lanthanum compound, a cerium compound and ayttrium compound in a range from 1/20 to 1/2 mol, in relation to one molof metal component in the ruthenium compound.

[0029] (6) A method of producing an electrode for use in hydrogengeneration, comprising the steps of applying onto a conductive base amixture comprising at least one type of platinum group compound andthermally decomposing the applied mixture in the presence of an organicacid to form a coating layer on the conductive base.

[0030] (7) An electrode for use in hydrogen generation obtainable by themethod described above in (6).

[0031] (8) A method of producing an electrode for use in hydrogengeneration, comprising the steps of applying onto a conductive base amixture comprising at least one type of platinum group compound and atleast one type of compound selected from the group consisting of alanthanum compound, a cerium compound and a yttrium compound, andthermally decomposing the applied mixture in the presence of an organicacid to form a coating layer on the conductive base.

[0032] (9) The method of producing an electrode for use in hydrogengeneration described above in (8), wherein the amount of at least onetype of compound selected from the group consisting of a lanthanumcompound, a cerium compound and a yttrium compound falls within a rangefrom 1/20 to 1/2 mol in relation to one mol of metal component in theabove described platinum group compound and the amount of the organicacid falls within a range from 1/20 to 2 mol in relation to one mol ofthe metal component in the platinum group compound.

[0033] (10) The method of producing an electrode for use in hydrogengeneration described above in any one of (6), (8) and (9), wherein theabove described platinum group compound is a ruthenium compound and theorganic acid is oxalic acid.

[0034] (11) The method of producing an electrode for use in hydrogengeneration described above in any one of (6) and (8) to (10), whereinthe pyrolysis is conducted in an oxygen atmosphere.

[0035] The electrode of the present invention is used as an activecathode in chlor-alkali electrolysis based on the ion exchange method.Additionally, the active cathode of the present invention is suitablyused particularly in a zero-gap type chlor-alkali electrolysis vesselbased on an ion exchange membrane method, maintains a low overvoltageover a long period of time and is excellent in durability, and canprevent the deterioration of the ion exchange membrane because theelution from the electrode is low at the termination of the electrolysisvessel operation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 shows an X-ray diffraction chart obtained before and afterelectrolysis for the coating layer composed of the pyrolysis products ofruthenium chloride and oxalic acid in Example 1;

[0037]FIG. 2 shows an X-ray diffraction chart obtained before and afterelectrolysis for the coating layer composed of the pyrolysis product ofRuCl₃+CeCl₃+oxalic acid in Example 3;

[0038]FIG. 3 shows a transmission electron micrograph of a section ofthe cathode coating layer of Example 3 after energization;

[0039]FIG. 4 shows an X-ray diffraction chart obtained before and afterelectrolysis for the coating layer composed of the pyrolysis product ofRuCl₃ in Comparative Example 1; and

[0040]FIG. 5 shows an X-ray diffraction chart obtained before and afterelectrolysis for the coating layer composed of the pyrolysis product ofRuCl₃+CeCl₃ in Comparative Example 2.

BEST MODE FOR CARRYING OUT THE INVENTION

[0041] Because the conductive base is used in a high concentrationalkali aqueous solution, it may be made of a stainless steel, but ironand chromium are eluted from a stainless steel electrode and theconductivity of a stainless steel is of the order of 1/10 that of nickelso that it is preferable to use nickel.

[0042] The base shape is not particularly limited, and an appropriateshape can be chosen according to the purpose in such a way that a porousplate shape, an expanded shape and a woven mesh shape formed by weavingnickel wire are preferably used. As for the base shape, an appropriateshape is dependent on the distance between the anode and cathode; whenthe distance is finite, either a porous plate shape or an expanded shapeis used, while when the membrane and the electrodes contact each other,namely, a zero gap electrolysis vessel is used, a woven mesh made byweaving thin wire or the like is used.

[0043] It is preferable that these bases are annealed in an oxidativeatmosphere to alleviate the residual stress because the residual stressgenerated at the time of fabrication still remains. Additionally, forthe purpose of forming the coating layer on the base surface in anadhering manner, it is preferable to form irregularities on the basesurface by the use of a steel grid or alumina powder and thereafter thesurface area is increased by the acid treatment.

[0044] The roughness degree of the surface is not particularlyspecified, but it is desirable that preferably the JIS surface roughnessof Ra=1 to 10 μm be employed, because the base is sometimes used in sucha manner that it contacts the ion exchange membrane. Accordingly, it ispreferable that blasting is conducted by use of an alumina powder of 100μm or less in average particle size, or an acid treatment is conducted.As the acid, preferably used are the inorganic acids includinghydrochloric acid, nitric acid, sulfuric acid and phosphoric acid, amongwhich sulfuric acid is preferably used owing to easier handling. It ispreferable that the acid treatment is conducted at a temperature fallingwithin the range from 60 to 90° C. with an aqueous sulfuric acid of 10to 50 wt % for 1 to 8 hours.

[0045] It is preferable that as the pretreatment of the base, an aqueoussolution containing 0.001 to 1% of surfactant is applied thereon anddried, and then a coating solution as described below is appliedthereon. The pretreatment improves the wettability of the base surfaceand base surface irregularities so that the coating solution can beapplied evenly even in the interior portions of the irregularities;accordingly, at the time of calcination in the air, the electrode activematerial is formed even in the interior portions of the irregularitiesin the base surface. This conceivably provides the effect of increasingthe surface area and the effect of improving the adhesiveness betweenthe electrode active material, that is, the electrode coating layer andthe electrode base.

[0046] The surfactant used in the above described pretreatment may beany type of the anionic, cationic and nonionic types, and actually anonionic surfactant is preferably used. The amount of the surfactant canbe small such that a 0.1 to 0.01% aqueous solution is preferably used.

[0047] The platinum compound used as the component in the coatingsolution is selected from the Pt compounds, Ir compounds, Ru compounds,Rh compounds, Pd compounds and Os compounds; the ruthenium compounds aremost preferable. The platinum group compound used as the component inthe coating solution can be any form of chloride, sulfate and nitrate;the chlorides are preferably used in view of the ease in pyrolysis andthe ease in the availability of the raw salts thereof. The metalconcentration in a platinum group compound is not particularly limited,but preferably falls within the range from 10 to 200 g/L, morepreferably within the range from 50 to 120 g/L, in view of the thicknessof the coating layer in one application.

[0048] Any forms of the lanthanum compounds, cerium compounds andyttrium compounds can be used, but the metal salts such as nitrates,sulfates and chlorides are preferable, and the chlorides are used morepreferably in view of the ease in pyrolysis and the ease in theavailability of the raw salts thereof. The substance having the effectof creating the reductive atmosphere at the time of pyrolysis is the onehaving carbon such as oxalic acid, formic acid, acetic acid, citric acidand the like, among which oxalic acid is preferably used. The two formsof anhydrate and dihydrate exist for oxalic acid, among which thedihydrate is preferably used in view of the ease of availablilty.

[0049] An organic acid can be added to a solution of a mixturecontaining a platinum group compound and at least one type of compoundselected from the group consisting of lanthanum compounds, ceriumcompounds and yttrium compounds, or an organic acid can be placed in thefurnace at the time of pyrolysis instead of adding to the solution ofthe mixture. However, it is desirable that the organic acid is mixedwith a platinum group compound and at least one type of compoundselected from the group consisting of lanthanum compounds, ceriumcompounds and yttrium compounds. Other solutions can be added to thesolution of the mixture. The mixture may remain partially asprecipitates in the solution. Such solutions include water, variousalcohols including propyl alcohol, butyl alcohol and allyl alcohol andother solvents, and have only to be those that can dissolve or suspendthe mixture. It is most preferable that the solution is either anaqueous solution or a suspension in water.

[0050] As for the mixture containing an organic acid, a platinum groupcompound and at least one type of compound selected from the groupconsisting of lanthanum compounds, cerium compounds and yttriumcompounds, it is preferable that the amount of the organic acid fallswithin the range from 1/20 to 2 mol and the amount of cerium fallswithin the range from 1/20 to 1/2 mol in relation to one mol of themetal component in the platinum group compound, in order for thecomponents of the mixture to be thermally decomposed and for the coatinglayer to display a sufficient effect.

[0051] When the amount of the organic acid is smaller that 1/20 mol inrelation to one mol of the metal component in the platinum groupcompound, the reduction prevention effect of the organic acid is notsufficient in the coating layer, while when the amount is larger than 2mols, precipitates and the like are generated in preparation of thecoating solution. Preferably, the amount of the organic acid fallswithin the range from 1/10 to 1 mol and the amount of cerium fallswithin the range from 1/8 to 1/4 mol in relation to one mol ofruthenium.

[0052] As the method for applying onto the conductive base the mixturecontaining an organic acid, a platinum group compound and at least onetype of compound selected from the group consisting of lanthanumcompounds, cerium compounds and yttrium compounds, preferably used are adip method in which the base is dipped into the coating solution, abrushing method in which the base is brushed with a coating solution, aroller method in which the coating is made with a sponge-like rollerimpregnated with the coating solution, and an electrostatic coatingmethod in which the coating solution is sprayed in such a way that thecoating solution and the base are charged with opposite charges.

[0053] Among these methods, the roller method and the electrostaticmethod are preferably used because these two methods are high inproductivity and permit an even application of the coating solution.

[0054] The coating solution is applied onto the base, then the base isdried at a temperature of the order of 10 to 50° C., and the pyrolysisis conducted with the base placed in a muffle furnace heated to 300 to650° C. The pyrolysis means a reaction in which the mixture containingprecursors is heated for the purpose of accelerating the decomposition;here the pyrolysis means a reaction in which the metal salt isdecomposed into the metal and gaseous substances. Specifically, thepyrolysis means the following reactions: if the metal salt is achloride, the salt is decomposed into the metal and chlorine gas; if themetal salt is a compound derived from nitric acid, the salt isdecomposed into the metal, and nitrogen and NOx gases; and if the metalsalt is a compound derived from sulfuric acid, the salt is decomposedinto the metal, sulfur, and SOx gases. On one hand, as for the metals,the reactions involved depend on the reaction atmosphere, and manymetals tend to be bonded to oxygen and thereby to form oxides in theoxygen atmosphere. The oxygen atmosphere means an atmosphere in whichoxygen is contained, and the most preferable oxygen atmosphere is theair in view of the production cost.

[0055] In order to accelerate the pyrolysis of the mixture containing anorganic acid, at least one type of platinum group compound and at leastone type of compound selected from the group consisting of lanthanumcompounds, cerium compounds and yttrium compounds, it is preferable thatthe pyrolysis temperature falls within the range from 450 to 600° C. Attemperatures lower than 450° C., the pyrolysis rate of the mixture isslow, while at temperatures higher than 600° C., the softening of thenickel base is sharply promoted. Accordingly, in view of theacceleration of the mixture pyrolysis and the maintenance of the nickelbase strength, the temperature range from 500 to 550° C. is mostpreferable. It is preferable that the time duration of the pyrolysis islong for the purpose of thermally decomposing to a full extent, but inview of the prevention of the thermally decomposed products from beingfully oxidized and the productivity of the electrode, the pyrolysis timeduration for one run of pyrolysis preferably falls within the range from5 to 60 minutes, more preferably from 10 to 30 minutes.

[0056] The pyrolysis forms the coating layer on the conductive base. Theprescribed thickness of the coating layer is obtained by repeatingaccording to need the cycle of application, drying and pyrolysiscalcination. The thicker is the coating layer, the longer is the periodover which a low overvoltage can be maintained; however, it ispreferable that the thickness of the coating layer is 1 to 5 μm from theviewpoint of economic efficiency. The coating weight is preferably 6 gto 30 g per an apparent surface area of 1 m², more preferably 2 to 3 μm,that is, 12 to 18 g per an apparent area of 1 m² as the coating amount.

[0057] For the purpose of attaining a prescribed thickness, the coatingamount in one application may be increased or the metal concentration ofthe platinum group compound may be increased; however, with a largecoating amount, coating unevenness may possibly occur at the time ofapplication and thus a nonuniform coating layer may be formed, and henceit is preferable that several cycles of application-drying-pyrolysiscalcination are conducted. The coating layer thickness attained in onecycle is preferably regulated to be of the order of 0.1 to 0.7 μm, morepreferably to be 0.2 to 0.4 μm.

[0058] It is preferable that calcination is conducted for a long timeduration for the purpose of stabilizing the coating layer, after thecoating layer of a prescribed thickness has been formed so that thepyrolysis of the coating layer may be fully conducted. The calcinationconditions specify the temperature range to be from 500 to 650° C.,preferably from 500 to 550° C. With a short time duration of the coatinglayer pyrolysis, the pyrolysis of the coating layer does not proceed toa full extent, while with too long a time duration, the reduction effectof the organic acid fades away and accordingly the oxidation of thecoating layer proceeds unpreferably. Thus, a reasonable time durationfor pyrolysis is of the order of 30 minutes to 8 hours, and preferablyfalls in the range from one hour to 3 hours.

[0059] As a coating layer, on a conductive base is provided acomposition which is obtained by thermally decomposing in the presenceof an organic acid the mixture containing at least one type of platinumgroup compound (preferably a ruthenium compound) and at least one typeof compound selected from the group consisting of lanthanum compounds,cerium compounds and yttrium compounds.

[0060] The effect of an organic acid (preferably oxalic acid) is toimprove the durability through small structural changes of the structureeven when the organic acid is used in a hydrogen reduction atmospherebecause the generation of such oxides that are high in crystallinity andeasily reduced in a hydrogen reduction atmosphere so as to tend to causestructural changes in scarce. X-ray diffraction measurement changesobserved before and after electrolysis in the coating layer itself aresmall. Even in the calcination in an atmosphere containing a largeamount of oxygen, the generation of oxides that are easily reduced inthe hydrogen atmosphere formed in the actual operation of electrolysisis scarce. Consequently, it is conceivable that on the conductive baseis formed a composition that is evidently different from a compositionobtained by pyrolysis in the absence of an organic acid.

[0061] The substance (preferably a cerium compound) selected from thegroup consisting of lanthanum compounds, cerium compounds and yttriumcompounds itself is low in hydrogen generation activity, but the oxidederived from that substance is converted from particle shapes to needleshapes in the environment where hydrogen is generated, and the needleshaped form plays the role of maintaining the coating layer made of aplatinum group compound and has an effect of suppressing the physicalexfoliation of the coating layer.

[0062] The coating layer is structurally stable even in the reductiveatmosphere where hydrogen is generated because the layer has the effectof suppressing the generation of the platinum group oxides and theeffect of converting the forms of such poorly active compounds aslanthanum oxide, cerium oxide and yttrium oxide during electrolysis;thus, the physical exfoliation of the coating layer can be suppressed,and the low overvoltage can be maintained over a long period of time.The involvement of an organic acid at the time of pyrolysis makes itpossible to conduct calcination in the air which is useful from anindustrial viewpoint.

[0063] <Determination of Ruthenium Oxide in the Coating Layer>

[0064] In the case where ruthenium oxide is selected as a platinum groupcompound, the quantity of the ruthenium oxide in the coating layer isdetermined as follows.

[0065] A sample in which a coating layer is formed on a nickel base isplaced in the sample holder of an X-ray diffraction measurementapparatus, and measurement is conducted with a Co X-ray tube or a CuX-ray tube. Then, the intensities of the most intense peaks of rutheniumoxide and nickel are compared. Specifically, a peak area is obtainedfrom the peak height multiplied by the half maximum full width, and theintensities thus obtained are compared. Here, the half maximum fullwidth means the diffraction line width at the 50% height of the peakintensity. With a Co X-ray tube, the most intense line of nickel isfound around 2θ=52° and the most intense line of ruthenium oxide isfound around 2θ=32.6°, where θ denotes the diffraction angle.

[0066] The intensity ratio between ruthenium oxide and the nickel of thebase is preferably 5/100 or less, more preferably 1/100 or less. Whenthe intensity ratio between ruthenium oxide and the nickel of the baseis larger than 5/100, the content of ruthenium oxide becomes large, andaccordingly the structural change is caused by the reduction ofruthenium oxide occurring in the reductive atmosphere where hydrogen isgenerated strongly, leading to exfoliation of the coating layer. Thereason for the exfoliation of the coating layer is not clear, but may beascribable to the structural change probably inducing crystal structurechange and generating strains in the crystal. Actually, in a cathodewhich has a large content of ruthenium oxide, the exfoliation of thecoating layer is confirmed when observation is made with an electronmicroscope after energization.

[0067] <Measurement of the Electrode Overvoltage>

[0068] The overvoltage of the cathode, with the coating layer formedthereon, for use in hydrogen generation is measured by the followingmethod.

[0069] A piece of cathode of 48×58 mm in size is cut out, and two holesare bored in the piece for the purpose of fixing the piece in a smallcell with nickel screws. An electrode formed by applying a coating ontoan expanded base can be subjected to evaluation as it is; a piece ofwoven mesh made of thin wire is fixed onto an expanded base having nocoating film thereon by use of thin nickel wire or the like and thensubjected to measurement. A reference electrode can be a string of PFA(tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) coatedplatinum wire with about 1 mm long of exposed platinum portion, fixedonto an electrode surface facing the ion exchange membrane.

[0070] The anode used is a so-called DSA composed of ruthenium oxide,iridium oxide and titanium oxide formed on a titanium base, and EPDM(ethylene propylene diene) rubber gaskets are used as the anode cell andthe cathode cell between which a sheet of ion exchange membrane issandwiched to conduct electrolysis. The type of the ion exchangemembrane is not particularly limited; however, it is preferable toconduct electrolysis by use of a cation exchange membrane “Aciplex®” foruse in sodium chloride electrolysis manufactured by Asahi Kasei Corp.

[0071] In the electrolysis, a current pulse generator is used as therectifier for electrolysis, the current is made to flow with aprescribed current density, the current is instantaneously turned offwhen the resulting wave form is observed on an analyzing recorder or thelike, and thus the overvoltage is derived by subtracting the solutionresistance between the electrode concerned and the reference electrode.

[0072] The electrolysis conditions are as follows: the current density:3 kA/m² or 4 kA/m²; the brine concentration in the anode chamber: 205g/L; the alkali concentration in the cathode chamber: 32 wt %; and theelectrolysis temperature: 90° C. For the purpose of confirming thelong-term stability of the electrolysis, the cathode overvoltagemeasurement is performed after 30 days have elapsed from the start ofthe electrolysis. The weight change of the coating layer is derived asfollows: the screws fixing the electrode are loosened to unfix theelectrode after the electrolysis has been terminated, the unfixedelectrode is fully washed with water and dried, and the weight thereofis measured; thus the weights before and after electrolysis arecompared.

[0073] Description will be made below with reference to Examples, butthe present invention is not limited to the Examples.

EXAMPLE 1

[0074] An electrode-shaped nickel expanded base, in which the short wayof aperture dimension SW was 3 mm, the long way of aperture dimension LWwas 4.5 mm, the feed pitch for expansion processing was 0.7 mm, and theplate thickness was 0.7 mm, was calcined at 400° C. for 3 hours in theair and an oxide coating layer was thereby formed on the surfacethereof. Subsequently, blasting with an alumina powder of 100 μm or lessin weight average particle size was conducted to provide the basesurface with irregularities. Then, the base was subjected to acidtreatment in 25 wt % sulfuric acid at 90° C. for 4 hours, and the basesurface was provided with finer irregularities.

[0075] In the next place, the nickel base was soaked into a solution inwhich a surfactant “Nonion N210” (trade mark: a nonionic surfactantmanufactured by NOF Corp. (Nippon Yushi K.K.)) was dissolved in water inthe ratio of 0.15 g of the surfactant to 200 g of water, and then thebase was taken out and dried in the air.

[0076] Then, oxalic acid dihydrate was added to a ruthenium chloridesolution in 6% hydrochloric acid with a metal concentration of 100 g/Lin such a way that the molar amount of oxalic acid dihydrate was 0.5times the molar amount of ruthenium, and the mixture thus obtained wasstirred at 90° C. for one day to yield a mixture composed of rutheniumchloride and oxalic acid.

[0077] Subsequently, the nickel base was soaked into the mixture, andthen dried at 50° C. for 10 minutes and calcined at 500° C. for 10minutes in the air. Then, a combined process of the soaking into thesolution containing oxalic acid and ruthenium, drying and calcination at500° C. was repeated 5 times in total, and then the base was calcined at550° C. for one hour.

[0078] The cathode as it was in this condition was cut into a piece of48×58 mm, the piece was fixed in a small cell and subjected to theovervoltage evaluation. The cathode piece cut into the size of 48×58 mm,for the purpose of making the piece removable, was fixed to the rib ofthe nickel cell body with nickel screws. As the reference electrode, aPFA coated platinum wire, fixed longitudinally, with an about 1 mm longexposed platinum portion was used. The anode used was a so-called DSAcomposed of ruthenium oxide, iridium oxide and titanium oxide formed ona titanium base, the anode cell and the cathode cell used were EPDM(ethylene propylene diene) rubber gaskets, and the ion exchange membraneused was “Aciplex®” F4203 manufactured by Asahi Kasei Corp.

[0079] In the electrolysis, a current pulse generator “HC114™”manufactured by Hokuto Denko Co., Ltd. was used as the rectifier forelectrolysis. The electrolysis conditions were as follows: the currentdensity: 4 kA/m²; the brine concentration in the anode chamber: 205 g/L;the alkali concentration in the cathode chamber: 32 wt %; and theelectrolysis temperature: 90° C. The cathode overvoltages after 3 daysand 30 days elapsed from the start of the electrolysis were measured.The cathode overvoltages were derived as follows.

[0080] The cathode voltage E1 against the platinum wire at the currentdensity of 4 kA/m² was measured, and then the voltage E2 was measured atthe time when the current was instantaneously turned off by means of thecurrent pulse generator “HC114™” manufactured by Hokuto Denko Co., Ltd.E2 corresponded to the measured voltage associated with the structuralresistance and solution resistance. Thus, the net overvoltage wasderived as E1-E2.

[0081] The weight change was derived as follows: the screws fixing theelectrode were loosened to unfix the electrode after the electrolysishad been terminated, the unfixed electrode was fully washed with waterand dried, and the weight thereof was measured; thus the weights beforeand after electrolysis were compared.

[0082] Thus, after 3 days, the overvoltage was found to be 74 mV and theweight change was found to be 0 mg. The same cathode was successivelysubjected to the electrode evaluation and it was found that theovervoltage was 73 mV and the weight change was 1 mg even after 30 days,manifesting that a cathode that was low in overvoltage and excellent indurability was obtained.

[0083] Additionally, the X-ray diffraction pattern of the cathodespecimen was measured by use of a Rigaku-Denki Geiger flex 4036A2 X-raydiffractometer with a Co X-ray tube. The results obtained are shown inFIG. 1.

[0084] Before energization, the most intense peak of the nickel base wasfound around 52°, and no peaks of ruthenium oxide were found around 32°,42° and 65°. After energization, changes were scarcely found except forthe advent of the peaks due to nickel oxide around 44° and 51°, and noexfoliation of the coating layer was found in the electron micrographtaken after energization.

EXAMPLES 2 TO 6

[0085] An electrode-shaped nickel expanded base, in which the short wayof aperture dimension SW was 3 mm, the long way of aperture dimension LWwas 4.5 mm, the feed pitch for expansion processing was 0.7 mm, and theplate thickness was 0.7 mm, was calcined in the air at 400° C. for 3hours and an oxide coating layer was thereby formed on the surfacethereof. Subsequently, blasting with an alumina powder of 100 μm or lessin weight average particle size was conducted to provide the basesurface with irregularities. Then, the base was subjected to acidtreatment in 25 wt % sulfuric acid at 90° C. for 4 hours, and the basesurface was provided with finer irregularities.

[0086] In the next place, the nickel base was soaked into a solution inwhich a surfactant “Nonion N210” (trade mark: a nonionic surfactantmanufactured by NOF Corp. (Nippon Yushi K.K.)) was dissolved in water inthe ratio of 0.15 g of the surfactant to 200 g of water, and then thebase was taken out and dried in the air.

[0087] Then, oxalic acid dihydrate was added to a ruthenium chloridemixture having a metal concentration of 100 g/L in such a way that themolar ratio of oxalic acid dihydrate took the values specified in Table1 in relation to one mol of ruthenium, then additionally cerium chloridewas added in such a way that the molar ratio of cerium took the valuesspecified in Table 1 in relation to one mol of ruthenium, and themixture thus obtained was stirred at 90° C. for one day to yield amixture composed of ruthenium chloride, cerium chloride and oxalic acid.

[0088] Subsequently, the nickel base was soaked into the mixture, andthen dried at 50° C. for 10 minutes and calcined at 500° C. for 10minutes in the air. Then, a combined process of the soaking into themixture, drying and calcination at 500° C. was repeated 10 times intotal, and finally the base was calcined at 550° C. for one hour. Thethickness of the coating layer after calcination was 2 to 3 μm.

[0089] The cathode as it was in this condition was cut into a piece of48×58 mm, the piece was fixed in a small cell and subjected to theovervoltage evaluation. The cathode piece cut into the size of 48×58 mm,for the purpose of making the piece removable, was fixed to the rib ofthe nickel cell body with nickel screws. As the reference electrode, aPFA coated platinum wire, fixed longitudinally on a surface contactingthe ion exchange membrane, with an about 1 mm long exposed platinumportion was used. The anode used was a so-called DSA composed ofruthenium oxide, iridium oxide and titanium oxide formed on a titaniumbase, the anode cell and the cathode cell used were EPDM (ethylenepropylene diene) rubber gaskets, and the ion exchange membrane used was“Aciplex®” F4203 manufactured by Asahi Kasei Corp.

[0090] In the electrolysis, the current pulse generator “HC114™”manufactured by Hokuto Denko Co., Ltd. was used as the rectifier forelectrolysis. The electrolysis conditions were as follows: the currentdensity: 3 kA/m²; the brine concentration in the anode chamber: 205 g/L;the alkali concentration in the cathode chamber: 32 wt %; and theelectrolysis temperature: 90° C. The cathode overvoltages after 30 dayshad elapsed from the start of the electrolysis were measured.

[0091] The cathode overvoltages were derived as follows. The cathodevoltage E1 against the reference electrode at the current density of 3kA m² was measured, and then the voltage E2 was measured at the timewhen the current was instantaneously turned off by means of the currentpulse generator HC114. E2 corresponded to the voltage associated withthe structural resistance and solution resistance. Thus, the netovervoltage was derived as E1-E2.

[0092] The weight change of the coating layer was derived as follows:the screws fixing the electrode were loosened to unfix the electrodeafter the electrolysis had been terminated, the unfixed electrode wasfully washed with water and dried, and the weight thereof was measured;thus, the weight changes were derived from the weights beforeelectrolysis and after 30 days of energization. The results obtained areshown in Table 1. TABLE 1 Example 2 3 4 5 6 Oxalic acid mol 1 1/2 1/41/2 1/10 Ce amount mol 1/4 1/4 1/4 1/8 1/4  Overvoltage mV 72  69 73 7471 Coating weight reduction mg 3  2  3  4  2

[0093] In the present Examples, as Table 1 shows, the overvoltages werelow and the weight reductions of the electrode coating layers weresmall, that is, electrodes high in durability were obtained.

[0094] The X-ray diffraction pattern of the cathode sample produced byusing the mixture of ruthenium 1 mol-oxalic acid 1/2 mol-Ce 1/4 mol inExample 2 was measured by means of a Rigaku-Denki Geiger flex 4036A2X-ray diffractometer with a Co X-ray tube. The results obtained areshown in FIG. 2.

[0095] Before energization, the most intense peak of the nickel base wasfound around 52°, and no peak of ruthenium oxide was found around 32°.After energization, changes were scarcely found except for the advent ofthe peaks due to nickel oxide around 44° and 51°, and no exfoliation ofthe coating layer was found in the electron micrograph taken afterenergization.

[0096] The cathode coating layer of a sample after 30 days ofenergization was peeled off from the expanded nickel base, and thesectional shape of the sample was subjected to conditioning and then toobservation on a transmission electron microscope. The electronmicrograph taken is shown in FIG. 3. The results of observationconfirmed the effect that cerium was converted into needle-shaped formsin the portions {circle over (1)} and {circle over (2)} in FIG. 3, andsuch needle-shaped particles play a role of holding the coating layer{circle over (3)} composed of ruthenium oxide and ruthenium hydrate sothat the exfoliation of the coating layer was suppressed.

[0097] The void found between {circle over (1)} and {circle over (3)} inFIG. 3 was formed when the sample for the transmission electronmicroscope observation was prepared, permitting a clear observation ofthe condition of the needle-shaped particles.

EXAMPLE 7

[0098] A woven mesh base made of a thin nickel wire of 0.15 mm indiameter with a mesh 50 aperture was calcined at 400° C. for 3 hours inthe air to form an oxide coating layer on the surface thereof.Subsequently, blasting with an alumina powder of 100 μm or less inweight average particle size was conducted to provide the base surfacewith irregularities. Then, the base was subjected to acid treatment in25 wt % sulfuric acid at 90° C. for 4 hours, and the base surface wasprovided with finer irregularities.

[0099] In the next place, the nickel base was soaked into a solution inwhich a surfactant “Nonion N210” (trade mark: a nonionic surfactantmanufactured by NOF Corp. (Nippon Yoshi K.K.)) was dissolved in water inthe ratio of 0.15 g of the surfactant to 200 g of water, and then thebase was taken out and dried in the air.

[0100] Then, oxalic acid dihydrate was added to a ruthenium chloridesolution in hydrochloric acid with a metal concentration of 100 g/L insuch a way that the amount of oxalic acid dihydrate was 0.5 mol inrelation to one mole of ruthenium, then further cerium chloride wasadded to the solution in such a way that the amount of cerium was 0.5mol in relation to one mol of ruthenium, and the mixture thus obtainedwas stirred at 90° C. for one day to yield a mixture composed ofruthenium chloride, cerium chloride and oxalic acid.

[0101] Application of a coating solution onto the woven mesh wasconducted by use of an application roller unit in which a vat containingthe coating solution was arranged at the undermost position in the unit,an application roller made of EPDM was impregnated with the coatingsolution, another roller was arranged above the EPDM roller so as toalways contact the EPDM roller, and further a roller made of PVC wasarranged above the roller positioned above the EPDM roller.

[0102] The base onto which the coating solution was applied was made topass between a pair of sponge rollers made of EPDM, quickly before thebase was dried, and the coating solution pooling in the intersectionpoints of the woven mesh was taken up and removed. Then, the woven meshbase was dried at 50° C. for 10 minutes, calcined in the air at 500° C.for 10 minutes, a combination of roller application, drying andcalcination at 500° C. was repeated 10 times in total, and thencalcination was conducted at 550° C. for one hour.

[0103] The cathode as it was in this condition was cut into a piece of48×58 mm, the piece was fixed in a small cell and subjected to theovervoltage evaluation. The cathode piece cut into the size of 48×58 mm,for the purpose of making the piece removable, was fixed onto anexpanded base having no coating film thereon by use of thin nickel wireor the like and then the base was fixed to the rib of the nickel cellbody with nickel screws. As a reference electrode, a PFA coated platinumwire, fixed longitudinally on a surface contacting the ion exchangemembrane, with an about 1 mm long exposed platinum portion was used. Theanode used was a so-called DSA composed of ruthenium oxide, iridiumoxide and titanium oxide formed on a titanium base, the anode cell andthe cathode cell used were EPDM (ethylene propylene diene) rubbergaskets, and the ion exchange membrane used was “Aciplex®” F4203manufactured by Asahi Kasei Corp.

[0104] In the electrolysis, the current pulse generator “HC114™”manufactured by Hokuto Denko Co., Ltd. was used as the rectifier forelectrolysis. The electrolysis conditions were as follows: the currentdensity: 3 kA/m²; the brine concentration in the anode chamber: 205 g/L;the alkali concentration in the cathode chamber: 32 wt %; and theelectrolysis temperature: 90° C. The cathode overvoltages after 30 dayselapsed from the start of the electrolysis were measured.

[0105] The cathode overvoltages were derived as follows. The cathodevoltage E1 against the reference electrode at the current density of 3kA/m² was measured, and then the voltage E2 was measured at the timewhen the current was instantaneously turned off by means of the currentpulse generator HC114. E2 corresponded to the voltage associated withthe structural resistance and solution resistance. Thus, the netovervoltage was derived as E1-E2.

[0106] The weight reduction of the coating layer was derived as follows:the screws fixing the electrode were loosened to unfix the electrodeafter the electrolysis had been terminated, the unfixed electrode wasfully washed with water and dried, and the weight thereof was measured;thus, the weight reduction was derived from the weights beforeelectrolysis and after 30 days of energization.

[0107] After 30 days from the start of the electrolysis, the overvoltagewas 68 mV, the coating weight reduction was 2 mg, and thus a cathode lowin overvoltage and high in durability was obtained.

COMPARATIVE EXAMPLE 1

[0108] A cathode was produced on the basis of the same operations asthose in Example 1, except that a ruthenium chloride solution in 6%hydrochloric acid with a metal concentration of 100 g/L was used.

[0109] In other words, an electrode-shaped nickel expanded base, inwhich the short way of aperture dimension SW was 3 mm, the long way ofaperture dimension LW was 4.5 mm, the feed pitch for expansionprocessing was 0.7 mm, and the plate thickness was 0.7 mm, was calcinedat 400° C. for 3 hours in the air and an oxide coating layer was therebyformed on the surface thereof. Subsequently, blasting with an aluminapowder of 100 μm or less in weight average particle size was conductedto provide the base surface with irregularities. Then, the base wassubjected to acid treatment in 25 wt % sulfuric acid at 90° C. for 4hours, and the base surface was provided with finer irregularities.

[0110] In the next place, the nickel base was soaked into a solution inwhich a surfactant “Nonion N210” (trade mark: a nonionic surfactantmanufactured by NOF Corp. (Nippon Yushi K.K.)) was dissolved in water inthe ratio of 0.15 g of the surfactant to 200 g of water, and then thebase was taken out and dried in the air.

[0111] In the next place, the nickel base was soaked into the rutheniumchloride solution in 6% hydrochloric acid with a metal concentration of100 g/L, dried at 50° C. for 10 minutes, and then calcined at 500° C.for 10 minutes in the air. Subsequently, a combination of the soakinginto the ruthenium chloride solution, drying and calcination at 500° C.was repeated 5 times in total, and then calcination was conducted at550° C. for one hour.

[0112] The cathode as it was in this condition was cut into a piece of48×58 mm, the piece was fixed in a small cell and subjected to theovervoltage evaluation. The cathode piece cut into the size of 48×58 mm,for the purpose of making the piece removable, was fixed to the rib ofthe nickel cell body with nickel screws.

[0113] As the reference electrode, a PFA coated platinum wire, fixedlongitudinally, with an about 1 mm long exposed platinum portion wasused. The anode used was a so-called DSA composed of ruthenium oxide,iridium oxide and titanium oxide formed on a titanium base, the anodecell and the cathode cell used were EPDM (ethylene propylene diene)rubber gaskets, and the ion exchange membrane used was “Aciplex®” F4203manufactured by Asahi Kasei Corp.

[0114] In the electrolysis, the current pulse generator “HC114™”manufactured by Hokuto Denko Co., Ltd. was used as the rectifier forelectrolysis. The electrolysis conditions were as follows: the currentdensity: 4 kA/m²; the brine concentration in the anode chamber: 205 g/L;the alkali concentration in the cathode chamber: 32 wt %; and theelectrolysis temperature: 90° C. The cathode overvoltage after 3 dayselapsed from the start of the electrolysis was measured.

[0115] The cathode overvoltage was derived as follows.

[0116] The cathode voltage E1 against the platinum wire at the currentdensity of 4 kA/m² was measured. The voltage E1 involves the cathodeovervoltage, the solution resistance between the reference electrode andthe cathode, the nickel cell structure resistance and the contactresistance between the electrode and the rib. Then, the voltage E2 wasmeasured at the time when the current was instantaneously turned off bymeans of the current pulse generator “HC114”. When the current isinstantaneously turned off, the cathode overvoltage is instantaneouslylowered, and the voltage E2 becomes the voltage associated with theabove described solution resistance, structural resistance and contactresistance, and thus the net overvoltage was derived as E1-E2.

[0117] The weight change before and after electrolysis was derived asfollows: the screws fixing the electrode were loosened to unfix theelectrode after the electrolysis had been terminated, the unfixedelectrode was fully washed with water and dried, and the weight thereofwas measured; thus the weights before and after electrolysis werecompared.

[0118] From these results, the overvoltage was found to be 75 mV and theweight was found to be reduced by 20 mg. The same cathode wassuccessively subjected to the electrolysis evaluation, and after 30days, the overvoltage was found to be 82 mV and the additional weightreduction was found to be 22 mg.

[0119] The X-ray diffraction chart obtained with a Co X-ray tube isshown in FIG. 4. Before energization, the most intense peak of thenickel base was found around 52°, a peak of ruthenium oxide was foundaround 32°, and other peaks of ruthenium oxide were found around 42° and65°; the calculated peak intensity ratio was 50/100, showing that thecontent of ruthenium oxide is larger. After energization, the peaksother than those of the nickel base around 61° and 52° practicallydisappeared.

[0120] The observation of the sample after energization with an electronmicroscope led to the confirmation of the phenomenon that the electrodecoating layer was physically exfoliated from the base surface. Theexfoliation from the electrode surface probably led to the reduction ofthe coating layer weight.

COMPARATIVE EXAMPLE 2

[0121] A cathode was produced on the basis of the same operations asthose in Examples 2-7, except that a ruthenium chloride aqueous solutionwith a concentration of 100 g/L and an aqueous solution of ceriumchloride were used.

[0122] In other words, a nickel base, in which the short way of aperturedimension SW was 3 mm, the long way of aperture dimension LW was 4.5 mm,the feed pitch for expansion processing was 0.7 mm, and the platethickness was 0.7 mm, was calcined at 400° C. for 3 hours in the air andan oxide coating layer was thereby formed on the surface thereof.Subsequently, blasting with an alumina powder of 100 μm or less inweight average particle size was conducted to provide the base surfacewith irregularities. Then, the base was subjected to an acid treatmentin 25 wt % sulfuric acid at 90° C. for 4 hours, and thus the basesurface was provided with finer irregularities.

[0123] In the next place, the nickel base was soaked into a solution inwhich a surfactant “Nonion N210” (trade mark: a nonionic surfactantmanufactured by NOF Corp. (Nippon Yushi K.K.)) was dissolved in water inthe ratio of 0.15 g of the surfactant to 200 g of water, and then thebase was taken out and dried in the air.

[0124] Then, cerium chloride was added to an aqueous solution ofruthenium chloride with a metal concentration of 100 g/L in such a waythat the content of cerium was 1/4 mol in relation to one mole ofruthenium, the mixture thus obtained was stirred at 90° C. for one day,and thus a mixture containing ruthenium chloride and cerium chloride wasprepared. Then, the nickel base was soaked into the mixture solution,and then dried at 50° C. for 10 minutes and calcined at 500° C. for 10minutes in the air. Then, a combination of the soaking into the mixture,drying and calcination at 500° C. was repeated 10 times in total, andfinally the base was calcined at 550° C. for one hour.

[0125] The cathode as it was in this condition was cut into a piece of48×58 mm, the piece was fixed in a small cell and subjected to theovervoltage evaluation. The cathode piece, cut into a piece of 48×58 mmfor the purpose of making the piece removable, was fixed to the rib ofthe nickel cell body with nickel screws.

[0126] As the reference electrode, a PFA coated platinum wire, fixedlongitudinally on a surface contacting the ion exchange membrane, withan about 1 mm long exposed platinum portion was used. The anode used wasa so-called DSA composed of ruthenium oxide, iridium oxide and titaniumoxide formed on a titanium base, the anode cell and the cathode cellused were EPDM (ethylene propylene diene) rubber gaskets, and the ionexchange membrane used was “Aciplex®” F4203 manufactured by Asahi KaseiCorp.

[0127] In the electrolysis, the current pulse generator HC114manufactured by Hokuto Denko Co., Ltd. was used as the rectifier forelectrolysis. The electrolysis conditions were as follows: the currentdensity: 3 kA/m²; the brine concentration in the anode chamber: 205 g/L;the alkali concentration in the cathode chamber: 32 wt %; and theelectrolysis temperature: 90° C. The cathode overvoltage after 30 dayshad elapsed from the start of the electrolysis was measured.

[0128] The cathode overvoltage was measured as follows. The cathodevoltage E1 against the reference electrode at the current density of 3kA/m² was measured, and then the voltage E2 was measured at the timewhen the current was instantaneously turned off by means of the currentpulse generator “HC114 ™”. E2 corresponded to the voltage associatedwith the structural resistance and solution resistance, and hence thenet overvoltage was derived as E1-E2.

[0129] The weight reduction of the coating layer was derived as follows:the screws fixing the electrode were loosened to unfix the electrodeafter the electrolysis had been terminated, the unfixed electrode wasfully washed with water and dried, and the weight thereof was measured;thus, the weight reduction was derived from the weights beforeelectrolysis and after 30 days from the start of energization. After 30days from the start of energization, the overvoltage was found to be 91mV and the weight was found to be reduced by 20 mg.

[0130]FIG. 5 shows the X-ray diffraction chart for Comparative Example 2obtained by use of a Co X-ray tube before and after energization.

[0131] According to the X-ray diffraction chart, before energization,the most intense peak of the nickel base was found around 52°, a peak ofruthenium oxide was found around 32°, and other peaks of ruthenium oxidewere found around 42° and 65°; the calculated peak intensity ratio wasof the order of 95/100, showing that the content of ruthenium oxide waslarge; it can be seen that after energization, the peaks other thanthose of the nickel base around 61° and 52° practically disappeared.

[0132] Additionally, the observation of the sample after energizationwith an electron microscope led to the confirmation of the phenomenonthat the electrode coating layer was physically exfoliated from the basesurface. The exfoliation from the electrode surface probably led to thereduction of the coating layer weight.

INDUSTRIAL APPLICABILITY

[0133] The electrode of the present invention is suitably used inchlor-alkali electrolysis, and is particularly suitably used in the zerogap electrolysis vessel in which the membrane and the electrodes contacteach other, whereby the electrode can maintain a low overvoltage over along period of time.

1. An electrode for use in hydrogen generation comprising a conductivebase and a coating layer formed thereon of a composition obtainable bythermally decomposing, in the presence of an organic acid, a mixturecomprising at least one type of platinum group compound.
 2. An electrodefor use in hydrogen generation comprising a conductive base and acoating layer formed thereon of a composition obtained by thermallydecomposing, in the presence of an organic acid, a mixture comprising atleast one type of platinum group compound and at least one type ofcompound selected from the group consisting of a lanthanum compound, acerium compound and a yttrium compound.
 3. The electrode for use inhydrogen generation according to claim 2, wherein the amount of one typeof compound, selected from the group consisting of a lanthanum compound,a cerium compound and a yttrium compound, falls within a range from 1/20to 1/2 mol in relation to one mol of metal component in said platinumgroup compound, and the amount of the organic acid falls within a rangefrom 1/20 to 2 mols in relation to one mol of the metal component in theplatinum group compound.
 4. The electrode for use in hydrogen generationaccording to any one of claims 1 to 3, wherein said platinum groupcompound is a ruthenium compound, and said organic acid is oxalic acid.5. An electrode for use in hydrogen generation comprising a conductivebase and a coating layer thereon, wherein said coating layer is acomposition obtainable by thermally decomposing, in an oxygenatmosphere, a mixture comprising a ruthenium compound, oxalic acid in arange from 1/20 to 2 mol and at least one type of compound selected fromthe group consisting of a lanthanum compound, a cerium compound and ayttrium compound in a range from 1/20 to 1/2 mol, in relation to one molof metal component in the ruthenium compound.
 6. A method of producingan electrode for use in hydrogen generation, comprising the steps ofapplying onto a conductive base a mixture comprising at least one typeof platinum group compound and thermally decomposing the applied mixturein the presence of an organic acid to form a coating layer on theconductive base.
 7. An electrode for use in hydrogen generation,obtainable by the method according to claim
 6. 8. A method of producingan electrode for use in hydrogen generation, comprising the steps ofapplying onto a conductive base a mixture comprising at least one typeof platinum compound and at least one type of compound selected from thegroup consisting of a lanthanum compound, a cerium compound and ayttrium compound in the presence of an organic acid to form a coatinglayer on the conductive base.
 9. The method of producing an electrodefor use in hydrogen generation according to claim 8, wherein the amountof at least one compound selected from the group consisting of alanthanum compound, a cerium compound and a yttrium compound fallswithin a range from 1/20 to 1/2 mol in relation to one mol of metalcomponent in said platinum group compound, and the amount of the organicacid falls within a range from 1/20 to 2 mol in relation to one mol ofthe metal component in the platinum group compound.
 10. The method ofproducing an electrode for use in hydrogen generation according to anyone of claims 6, 8 and 9, wherein said platinum group compound is aruthenium compound and the organic acid is oxalic acid.
 11. The methodof producing an electrode for use in hydrogen generation according toclaim 6 or any one of claims 8 to 10, wherein the pyrolysis is conductedin an oxygen atmosphere.